Accident Details
The accident occurred during a maintenance test flight after both engines had been replaced with higher horsepower models. The airplane had not been flown for approximately five months prior to the flight.
Witness Observations
Witnesses reported that the airplane departed and completed two uneventful touch-and-go landings. Subsequently, the aircraft was observed struggling to gain altitude and airspeed while maneuvering in the traffic pattern. One witness, an aircraft mechanic, noted that the airplane was yawing to the left and that he heard noises consistent with propeller pitch changes, which he believed were in the "Beta" range.
The Accident
The airplane stalled and impacted trees in a wooded marsh area, coming to rest about 80 degrees vertically. The accident site was located approximately one mile from the airport.
Wreckage Examination
Examination of the wreckage did not reveal any preimpact malfunctions. However, the lack of flight recorders and the condition of the wreckage precluded the gathering of additional relevant information. Damage observed to both engines and both propellers indicated they were likely operating at symmetrical power settings and blade angles at the time of impact, with any differences in scoring signatures likely resulting from impact damage.
Probable Cause
The official probable cause is that the pilot did not maintain airspeed while maneuvering, which resulted in an aerodynamic stall. The reason for the reported yawing and noise associated with propeller pitch changes prior to the stall could not be determined.